Chapter
Five
The theatre
We can easily trace the kinds of neural processing that must
have taken place. Reading the instructions would involve activ-
ity in much of the visual cortex and in language areas such as
Wernicke’s area. The oculomotor complex of nuclei would be
responsible for moving your eyes as you read, and motor cor-
tex for preparing and executing the skilled action of touching
thumb to nose. Frontal areas would be involved in planning
and making the decision whether to bother or not. When your
thumb touched your nose, parts of the sensory cortex mapped
for the hand and face would be activated, and connected with
ongoing activity maintaining the body schema (your sense of
where your body is in space). In principle, we could examine
this activity at any level of detail we wished. But where does the consciousness
happen? Two common metaphors imply answers: in one, consciousness is the
centre into which experiences come and from which commands go out; in the
other, there is a hierarchy of processing with a top where consciousness reigns
(see a critical commentary on hierarchies by Feinberg, 2001, pp. 124–125). Global
workspace theories of consciousness, to which we will turn later in this chapter,
exemplify the first of these; Semir Zeki’s hierarchy of micro-consciousnesses, with
a single unified macro-consciousness at the top (Chapter 6), is an example of the
second. When we talk about neural processing that is ‘top-down’ (driven by prior
goals, expectations, etc.) and ‘bottom-up’ (stimulus-driven), we might well be
drawn to assuming a centre or a top or both.
First, note the obvious point that there is no place in the brain to fit either of
these intuitions. As William James poetically put it, there is no ‘pontifical’ neuron
to which our consciousness is attached; ‘no cell or group of cells in the brain of
such anatomical or functional pre-eminence as to appear to be the keystone or
centre of gravity of the whole system’ (1890, i, pp. 179–180). More than a century
later, it is still tempting to think that there must be a centre or a top. But in terms
of brain activity, there is no centre and no single top (Zeki, 2001).
To make this clear, we may try to ask which processing is happening on the way
in, and which on the way out. Then we might find the middle – where input stops
and output begins. This is a reasonable way to think when dealing with a whole
organism. After all, light certainly goes into the eyes, and muscles move the arms
and legs. So, we can talk unproblematically about input and output. But now we
are going right inside the system. Maybe it is just a bad habit of thought, derived
from thinking about whole human beings, that leads us to believe that within the
brain, too, we can go on looking for ‘the middle’. In fact, there can be no middle.
Ask yourself whether the activity in Wernicke’s language comprehension area is
on the way in or the way out, or that in area V1 or V5, or in the temporal lobe. The
question makes no sense. There is not a single stream of neural activity coming
into a middle and sending a new stream out; there is massive parallel processing.
There are feedback loops, complex cell assemblies forming and dissolving, mutual
interactions between distant areas, and so on. There is plenty of integration but
there is no middle, and therefore also no top (a top being just a particularly priv-
ileged kind of middle).
Similarly, there is no special time at which consciousness happens. Certainly infor-
mation comes in first and actions happen later, but between the two there are
afferents efferents?
FIGURE 5.2 • Signals come in along afferent
nerves, and go out along efferent
nerves. So where is the middle,
where ‘I’ receive the impressions
and send out the orders? Descartes
thought it lay in the pineal gland.
According to Dennett, the question
betrays a commitment to the
Cartesian Theatre. There is no
middle, and no ‘great mental
divide’ between input and output
(Dennett, 1991, p. 109).